In searching of top conference in GIS, I found following websites fairly useful. Therefore, I compiled these links here for your reference.
Each of them may provide a little different interface for searching for events. Additionally, some events are in the field of computer science. But since gis and cs can never be separately mentioned, I include both here.
This site chronologically lists geospatial events, events, trainings, and workshops by month. Event submission information is available towards the end of this page. GIS webinars are noted with a location of "online" in the GIS conference and events listings after the map or you can visit the
GIS Webinar page
for a complete list of online GIS training and webinars.
Upcoming Conferences
A list view only maintained by Global Spatial Data Infrastructure Association.
This Google calendar is maintained by University of Zurich. A nice thing about using Google calendar is you can add it to your own Google calendar and as a result get automatic updates.
teca.co is a technical event search site that allows you to search technical events based on a specified location. Based on your search, it generates a calendar view with hyperlinks to each event in the calendar.